Polyacetal resins have excellent chemical resistance, and therefore molded articles having polyacetal resins as a raw material have been widely used in automobile components. For example, they are used as large scale components such as fuel delivery units and the like represented by fuel pump modules and the like which directly contact fuel oil.
In recent years, in order to respond to environmental regulations of various countries, sulfur reduction of fuels has been promoted. However, due to the very high cost of desulfurization facilities, in some countries high sulfur fuels are still in circulation. These high sulfur fuels, compared to low sulfur fuels, have a tendency to readily degrade polyacetal resins.
Incidentally, an injection molded article produced from a polyacetal resin will have residual stress inside the molded article resulting from the cooling when injection molding. When such an injection molded article contacts a high sulfur fuel or the like, cracks occur at locations where the residual stress is large, which may become the cause of trouble such as fuel leaks and the like. Accordingly, for countries where high sulfur fuel is in circulation, it is necessary to use as a raw material a resin material having a high resistance to high sulfur fuels.
As a polyacetal resin composition having a high acid resistance, a polyacetal resin composition comprising (A) 100 parts by weight of a polyacetal resin, (B) 0.1 to 3.0 parts by weight of a hindered phenol-based antioxidant, (C) 0.001 to 3.0 parts by weight of a nitrogen containing compound, (D) 0.1 to 3.0 parts by weight of a fatty acid calcium salt, and (E) 0.1 to 3.0 parts by weight of a lubricant has been proposed (for example, refer to Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2010-031200